Conventionally, there has been provided a compressor which includes a closed container, a compression element to be placed in the closed container, and a motor placed in the closed container to drive the compression element via a shaft (see JP S55-69180U)
Conventionally, the compression element includes first and second bearings for supporting a shaft, a cylinder to be placed between the first bearing and the second bearing, and a roller placed in the cylinder and fitted to the shaft.
The first bearing is placed closer to the motor than the second bearing. The first, second bearings each have an annular groove on an opposing surface opposed to an end face of the roller. In this case, the annular groove of the first bearing and the annular groove of the second bearing are equal in width to each other.
During operation of the above-described compressor, there may occur, from time to time, deflection of the shaft due to a gas load within the cylinder or other reasons, so that the shaft is brought into contact with the first, second bearings. Even in such a case, by the formation of the annular grooves, the first, second bearings are elastically deformed so that the contact of the shaft with the bearings can be made to be not point contact but plane contact. Thus, bearing pressures involved are reduced so that seizures are prevented.
In this connection, in order that lubricating oil present on the inner peripheral side of the roller is kept from leaking to the outer peripheral side of the roller through between an end face of the roller and the opposing surfaces of the first, second bearings, there has been a necessity for reducing the widths of the annular grooves to ensure seal lengths between the end face of the roller and the opposing surfaces of the first, second bearings.
For the conventional compressor shown above, since the width of the annular groove of the first bearing and the width of the annular groove of the second bearing are equal to each other, there has been a necessity for lessening both the width of the annular groove of the first bearing and the width of the annular groove of the second bearing.
However, machining of an annular groove of such a small width is a difficulty, and forming the annular grooves in both the first bearing and second bearing would take a long manufacturing time, leading to an increased manufacturing cost as a problem. Further, setting a larger depth for annular grooves to increase the elastic deformation of the first, second bearings would make it even more difficult to machine the annular grooves because of their small widths.
Moreover, with use of a low-priced sintered article for the material of the first, second bearings, machining of the annular grooves in the sintered article is impossible to fulfill because of high hardness of the sintered article, making it inevitable to use a casting article as the material of the first, second bearings. For example, for machining of the annular grooves with a cutting tool, the quantity of machinable casting articles per cutting tool was 100 to 200 pieces, while the quantity of machinable sintered articles was 5 pieces.
Thus, with the conventional compressor, it has been impossible to satisfy both the prevention of lubricating oil from leakage through between the bearings and the roller end face and the facilitation of formation of the annular grooves in the bearings at the same time.